Technical Field
The instant disclosure relates to a wafer cassette, in particular, to a wafer cassette capable of receiving wafers with two or more sizes.
Related Art
During the production of semiconductor elements, the received and conveying of wafers between different workstations are achieved by wafer cassettes. In general, twenty-five pieces of wafer are set as a lot; that is, a conventional wafer cassette is designed to receive twenty-five pieces of wafer with a uniform size (e.g., 6 inches, 8 inches, or 12 inches). When the wafer cassette is full, the wafers are then transmitted to the next workstation by manual operation or automatic transmission apparatuses. One of the reasons why the conventional wafer cassette receive wafers with one size is, each of the production lines in the wafer factory can process wafers with a uniform size during a time duration, and the production parameters of the production lines are needed to be reset when the size of the wafers to be processed changes. For maintaining a high production rate and a high defect-free rate, wafers with different sizes are not processed at the same time. As a result, although the wafers have diameters in 6 inches, 8 inches, or 12 inches, a single wafer cassette is adapted to receive wafers with a single size.
In addition, the reason why the size of the wafer cassette should be uniform is the numerous steps for processing wafers and the high automation procedures of wafer processing. During the production of semiconductor elements, the wafers to be processed are taken out from the wafer cassette by transmission devices, and then the wafers are placed to a to-be-processed area (or a to-be-detected area). Before the transmission device picks the wafer, the wafer cassette should be scanned by an optical equipment to determine the positions of the wafers with respect to the wafer cassette. As a result, the optical equipment may have to be redesigned otherwise the optical equipment may not determine the positions of the wafers correctly if wafers with different sizes are placed in the wafer cassette.